Threaded cap

ABSTRACT

A threaded cap is disclosed. The threaded cap may form a portion of a closure assembly comprising also comprising a threaded transition. The closure assembly may be utilized to seal a liquid containing bottle, particularly one containing a liquid fabric composition.

FIELD OF THE INVENTION

The present invention relates to threaded caps and to the threadedclosure assemblies of which they may form a part.

BACKGROUND OF THE INVENTION

Threaded caps and transitions are used in various industries as bottleclosures. The cap characteristics may impact the amount of force and/orthe number of cap revolutions required to seal or open a closed bottlewith the cap. Such characteristics include, but are not limited to thenumber of thread leads and the thread lead angle.

The importance of thread characteristics in the field of mass producedbottles is evident throughout the useful life of the bottle. Forexample, when bottles are initially made on high speed manufacturinglines, it is important for the caps to be rapidly registered andmutually engaged with the transition threads to close the bottle.Additionally, enough torque must be applied to the cap in order to forma seal between the cap and the transition, otherwise, the cap can backoff, allowing for the bottle contents to leak out during storage and/ortransport. Yet when the bottle reaches the consumer, he or she must beable to readily open the bottle, and in some instances, to reseal it forfuture use. These characteristics are of especial import in the area ofliquid laundry detergents given the frustrations that can be associatedwith being unable to dispense the liquid from the bottle, and/or theliquid leaking from the bottle to cause a mess.

Some commercially available caps, such as the cap 10 shown in FIG. 1,comprise one discontinuous thread 11, which necessarily has one lead 12.To close a bottle with this cap, it may be necessary to rotate the capas many as about 1.5 times. This can be undesirable for at least tworeasons. First, rotating a cap multiple times to close a bottle may notbe efficient as it can waste precious time on a high speed manufacturingline where every second counts. Second, it may make it difficult forindividuals with arthritis and other afflictions to effect the twistingmotion that is necessary to rotate the cap multiple times to obtain atight closure.

Some commercially available caps, such as the cap 20 shown on the bottle200 pictured in FIG. 2, are “top heavy”, meaning that when the bottle isclosed, the cap sticks out high above the bottle opening. Aside frombeing aesthetically unappealing, this can be undesirable from apractical standpoint, because it can require more shipping and shelfspace than a similar sized bottle having a shorter cap. One approach toovercoming these disadvantages would be to hold the volume of the capconstant, while expanding the diameter of the cap. This would result ina shorter, more squat cap. Yet when the same amount of liquid is placedin a shorter, squat cap, it may appear that less liquid is present thanin a taller cap having the same volume, but a smaller diameter. This canbe disadvantageous in the areas of compacted detergents since it maylead the consumer to assume that the dosage of a product is too skimpy.

Some commercially available caps, such as the cap 10 shown in FIG. 1 orthe cap 30 shown in FIG. 3, respectively comprise threads (11 and 31)adjacent to the cap membrane (17 and 37) that seals the cap against thebottle transition (not pictured). Moreover, there may be a shortdistance between the opening of the cap 14 and 34 and the respectivemembrane 17 and 37. These two characteristics, particularly whencombined, can make it difficult to mechanically or manually register thecap within the transition to engage the cap threads with the transitionthreads. This can be problematic on high speed manufacturing lines aswell as for those with impaired manual dexterity.

SUMMARY OF THE INVENTION

The present invention is directed to threaded closure assemblies thatsolve the aforementioned problems. The invention is also directed to thecaps themselves.

The threaded closure assembly may be utilized as a bottle closure,particularly of a bottle containing a liquid composition. The threadedclosure assembly comprises a cap and a transition. The cap is designedto be easily applied on a high speed manufacturing line with enoughforce to prevent leakage from the bottle, yet the cap is also easilyopened and resealed by the consumer. This is surprisingly achievedthrough the particular combination of two or more of the following:multiple thread leads; high thread lead angles; a proportionally longerdistance between the cap opening and cap membrane; and placing thethreads near to the cap opening rather than to the cap membrane.

In one embodiment, a threaded closure assembly comprises a transitionand a cylindrical cap. The transition in turn comprises a transitionwall that is described by an inner and outer transition wall surface. Atransition collar is attached to the transition wall. The transitioncollar itself comprises a transition collar rim.

The cap which is described by a longitudinal center axis comprises aclosed cap top distally attached to a substantially circular cap openingvia a cap wall. The cap wall is described by an inner cap wall surfaceand an outer cap wall surface. The outer cap wall surface has acircumference “C_(o)”. A substantially circular cap membrane is disposedon the outer cap wall surface. At least two external thread structuresare also disposed on either the inner or the outer cap wall surfacealong the longitudinal center axis of the cap between the substantiallycircular cap membrane and the substantially circular cap opening. Eachof the external threads has a discrete thread start disposed along theouter cap wall surface proximate to the substantially circular capopening. Each of the external threads has a thread lead angle of fromabout 4 to about 45 degrees and a length less than one half of C_(o).

The transition additionally comprises at least two internal threadstructures disposed on either the inner or the outer transition wallsurface. The internal threads are placed on the transition such thatthey are mutually engageable with the external thread structures on thecap. When the external and internal thread structures are engaged, thereis a seal between the circular cap membrane and the transition collarrim. This seal may be air tight and/or liquid tight.

Another embodiment relates to a method of sealing a bottle containing aliquid with a threaded closure assembly comprising a transition and acylindrical cap. The method comprises the following steps in any usefulorder:

-   -   (a) providing a bottle comprising a bottle body with a closed        end and an open end which terminates in a substantially circular        bottle mouth;    -   (b) functionally connecting the transition to the bottle mouth,        wherein the transition comprises:        -   i. a transition wall described by an inner transition wall            surface and an outer transition wall surface;        -   ii. a transition collar attached to the transition wall,            wherein the transition collar comprises a transition collar            rim; and        -   iii. at least two internal thread structures disposed on            either the inner or the outer transition wall surface;    -   (c) providing a cap being described by a longitudinal center        axis, the cap comprising:        -   i. a closed cap top distally attached to a substantially            circular cap opening via a cap wall having an inner cap wall            surface and an outer cap wall surface, the outer cap wall            surface having a circumference C_(o);        -   ii. a substantially circular cap membrane disposed on the            outer cap wall surface; and        -   iii. at least two external thread structures disposed on            either the inner or the outer cap wall surface along the            longitudinal center axis of the cap between the circular cap            membrane and the cap opening, wherein each of the at least            two external threads comprises:            -   1. a discrete thread start disposed along either the                inner or the outer cap wall surface proximate to the cap                opening;            -   2. a thread lead angle of from about 4.5 to about 45                degrees; and            -   3. a length less than one half of C_(o);    -   (d) inserting the substantially circular cap opening into the        transition; and (e) substantially rotationally engaging the        external and internal thread structures by turning the cap less        than 90° to form a seal between the circular cap membrane and        the transition collar rim. The seal may be air tight and/or        liquid tight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the cap of a prior art threaded closureassembly.

FIG. 2 is a perspective view of a prior art threaded closure assembly ona bottle.

FIG. 3 is a perspective view of the cap of a prior art threaded closureassembly.

FIG. 4 is a perspective view of a cap per the invention.

FIG. 5 is a bottom view of a cap per the invention.

FIG. 6 is a cross-sectional view of a cap per the invention.

FIG. 7 is a perspective view of a transition per the invention.

FIG. 8 is a cross-sectional view of a transition per the invention.

FIG. 9 is a cross-sectional view of a transition per the invention.

FIG. 10 is a cross-sectional view of a threaded closure assembly per theinvention.

FIG. 11 is a cross-sectional view of a threaded closure assembly per theinvention.

FIG. 12 is a perspective view of a bottle per the invention.

FIG. 13 is a perspective view of a bottle per the invention.

FIG. 14 is a perspective view of comparative and inventive caps havingdifferent thread configurations.

FIG. 15 is a plot of off-torque data.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “Overflow Volume” is the maximum volume ofliquid that a cap may hold without its contents overflowing.

As used herein, the term “Compacted” composition means a compositionthat water has been removed.

As used herein, the term “fluid” means any substance that is capable ofbeing poured. Fluids of the present invention include, but are notlimited to, liquids, fluidizable solids or powders, and granularcompositions that are capable of being poured.

As used herein, the term “cylindrical cap” means a cap having at least aportion thereof which may be described as having the form of a cylinderor tube. “Cylindrical cap” is not meant to exclude caps comprisingnon-cylindrical portions, such as for example a non-cylindrical, closedcap top.

A threaded closure assembly per the present invention comprises atransition and a cylindrical cap. Optionally, the threaded closureassembly may be functionally attached to the open mouth of a bottle viaa transition according to the present invention. The bottle may besealed through the mutual engagement of the cap and transition threads.

Any one or more of the cap, transition or bottle may be made from anysuitable material or combination of materials. Various plasticsmaterials are suitable including, but not limited to polyvinyl chloride,high and low density polyethylene, polypropylene, acrylic, polystyrene,polycarbonate, polyethylene terepthalate (PET), polyethylene napthalate(PEN) and copolymers and blends of these PET and PEN in both crystallineand amorphous forms.

It is contemplated that any one or more of the cap, transition or bottlemay be made using any suitable process including, but not limited to,blow molding techniques, such as stretch blow molding.

Each of the cap, transition and bottle are described in further detailbelow.

Cap

Referring to FIG. 4, the cylindrical cap 40 is described by alongitudinal center axis 80 and a line 81 orthogonal thereto. The caphas a closed top 43 that is distally attached to a substantiallycircular cap opening 44 via a cap wall 45. FIG. 5 presents analternative view of the cap 40 of FIG. 4. Specifically it is a view ofthe bottom of the closed cap top through the substantially circular capopening 44. Referencing FIG. 5, the cap wall 45 is described by an innercap wall surface 45 a and an outer cap wall surface 45 b. The inner capwall surface 45 a has a circumference “C,” and the outer cap wallsurface 45 b has a circumference “C_(o)”. Referring to FIG. 4 and FIG.5, a substantially circular cap membrane is 47 disposed on the outer capwall surface 45 b. The cap membrane may run along a circumference of theouter wall, such as along C_(o) in FIG. 5. In some embodiments, such asthe one depicted in FIG. 5, the membrane is continuous.

Referring to FIG. 4, three external thread structures 41 a, 41 b and 41c are disposed on the outer cap wall surface 45 b along the longitudinalcenter axis 80 of the cap 40 between the membrane 47 and the cap opening44. In some embodiments, there are at least two thread structures. Insome embodiments there are three or more thread structures. In theembodiment depicted in FIG. 4, there are three thread structures. Insome embodiments, there are four or more thread structures. Each threadstructure has a discrete thread start. In FIG. 4, only the discretethread starts 42 a and 42 b of the thread structures 41 a and 41 brespectively, are visible. These thread starts are located proximate tothe cap opening 44. The thread start may be less than about 5, less thanabout 4, less than about 3 or less than about 1 mm away from the capopening 44.

In some embodiments, the external thread structures may be disposed onan inner wall of the cap. Referring to FIG. 6, some cap embodiments maycomprise a double wall 250. In these embodiments, the external threadsmay be disposed on an inner wall 245 a of the double wall 250.

Each thread is characterized by a thread lead angle. Referring to FIG.4, the thread lead angle 50 is the angle θ formed at the theoreticalintersection of a line 51 drawn through the thread 41 b with the line 81orthogonal to longitudinal center axis 80 of the cap. Each thread on thecap may have the same or different thread lead angle. In someembodiments, each thread lead angle may have a value of from about 4 toabout 45 degrees, from about 5 to about 20 degrees, from about 4.5 toabout 15 degrees, from about 5.5 to about 10 degrees, or any combinationof upper and lower limits, or any upper or lower limit, or any number inbetween the upper and lower limits. It is presently believed that thatcap angles greater than 45 degrees may not be of use. Without wishing tobe bound by theory, if the thread lead angle is too great, the removaltorque can become so low, that the cap will simply back off on its owndue to internal forces. Consequently, there is a balance to be struckwith regard to thread lead angle of having an angle that is great enoughto reduce off-torque, but not so great as to loose the advantage of agood seal between the cap membrane and the transition collar rim.

Each thread may have the same or different lengths. In one embodiment,all of the threads have the same length. In another embodiment, all ofthe threads have the same length which is less than one half of the capouter wall circumference, C_(o).

Each thread may be continuous or discontinuous. In some embodiments, atleast one thread is continuous. In other embodiments, at least onethread is discontinuous. In some embodiments, there is a combination ofcontinuous and discontinuous thread(s).

In some embodiments, the cap may be used to meter doses of a liquid,i.e., it may function as a dosing cap. In some embodiments, the OverflowVolume of the cap is less than about 100 ml, less than about 85 ml, lessthan about 75 ml, less than about 65 ml or less than about 58 ml. Insome embodiments, the cap may comprise a fill line on the inner cap wallsurface, on the outer cap wall surface, or on both surfaces. In someembodiments there may be multiple fill lines that reflect differentcomposition dosing levels.

Transition

Referring to FIGS. 7, 8 and 9, the transition 400 is described by atransition wall having a transition inner wall surface 445 a and atransition outer wall surface 445 b. A transition collar 450 is attachedto the transition wall. The transition collar has a transition collarrim 451.

Referring to FIGS. 7 and 8, internal threads 441 are disposed on theinner wall surface. Referring to FIG. 9, the internal threads 441 aredisposed on the outer wall surface 445 b. The internal threads aredesigned to be mutually engageable with the external threads disposed onthe outer cap wall surface. The number of internal threads may be thesame as the number of external threads on the outer cap wall surface. Insome embodiments, there are three or more thread internal structures. Insome embodiments, there may be only one internal thread structure thatis configured such that the external threads of a cap may engage theinternal threads at multiple points. The latter embodiment is depictedin the cross-sectional view in FIG. 8, where there is one internalthread structure 441. In some embodiments, there are two or moreinternal thread structures.

The transition may optionally comprise a spout. Referring to FIG. 7, aspout 460 is functionally attached to the transition collar 450 via theinner wall surface 445 a of the transition. When the transition isattached to a bottle, the spout may function to direct the compositionthat is being poured out of the bottle. For example, if the bottlecontains a fluid composition, the spout functions to direct the fluidout of the bottle. Typically, the spout extends in a length beyond thecollar to prevent buildup of the composition in the transition head. Thespout extending beyond the collar may also aid in the pouring of thecomposition(s) from the bottle, particularly into a dosing cap.

In some embodiments, the transition may further comprise a dripconcentrator. A drip concentrator may be concentrically interposedbetween the spout and the transition wall. The drip concentratorfunctions to gather any composition remaining in the dispensing cup uponreapplication of the cup to the transition. Suitable drip concentratorsof use in the present invention are described in USPN 2009/063369.

Threaded Closure Assembly

FIG. 10 illustrates one embodiment of a threaded closure assembly 4000according to the invention. In FIG. 10, The cap 40, which comprisesexternal threads on the outer cap wall is shown as being transparent. Inthe figure, the external threads of the cap (not shown) and the internalthreads 441 located on the inner wall of the transition are mutuallyengaged such that a seal is formed between the circular cap membrane 47and the transition collar rim 451. The seal may be air and/or liquidtight.

FIG. 11 illustrates a cross-sectional view of another embodiment of athreaded closure assembly according to the present invention. In FIG.11, the cap 40, which comprises external threads 41 on the inner wallsurface 245 a of the double wall 250 is mutually engaged with theinternal threads 441 disposed on the outer wall surface 445 b of thetransition 400 such that a seal is formed between the circular capmembrane 47 and the transition collar rim 451. The seal may be airand/or liquid tight.

Referring to FIG. 10, when a seal is formed, the distance 480 betweenthe transition collar rim 451 and the closed cap top 43 may be measuredalong the longitudinal center axis 80 of the cap. In some embodiments,this distance is less than about 40, less than about 35 or less thanabout 30 millimeters (mm) The longer the distance, the more the threadedclosure assembly “sticks out” above the bottle to which it is attached.It is believed that distances higher than about 40, about 45 and aboveor about 50 mm and above are undesirable for at least three reasons.First, the higher the cap of the assembly sticks out above the bottle towhich it is attached, the more storage, shipping space and display spaceis required. Second, a high profile cap may not be as aestheticallyappealing as a lower profile one. Third, it is desirable to have more ofthe cap nested into the transition when it the seal is formed. In thisway, the cap walls between the cap opening and the cap membrane serve asa guide for seating the cup into the transition for engagement of theexternal and internal threads. This is particularly advantageous overthe prior art cap on a high speed assembly line, where the preciseline-up of the cap and transition are necessary. As respectively shownin FIGS. 1 and 3, on the prior art caps 10 and 30, there is very littlecap wall available as a guide for seating between the cap threads andcap membrane. This may result in a higher incidence of cross threading.

For any one or more of the aforementioned reasons, threaded closureassemblies of the present invention may comprise a distance along thelongitudinal center axis of the cup between the transition collar rimand the closed cap top that is about three, about four, greater thanabout 3, or greater than about 4 more times than the distance betweenthe substantially circular cap membrane and the substantially circularcap opening.

Bottle

FIG. 12 illustrates one embodiment of a bottle 90 according to theinvention. In this embodiment, the cap 40 comprises external threads onits outer wall surface and the transition 400 comprises internal threadson its inner wall surface (threads not shown). In this way, the outerwall of the transition remains visible when the cap and the transitionare mutually engaged such that the bottle is sealed.

In FIG. 12, the bottle has a closed end (not shown) distally locatedfrom an open end 92, which terminates in a substantially circular bottlemouth (not shown). The bottle mouth is functionally attached to athreaded closure assembly 4000 according to the present invention viathe transition. The attachment can be accomplished using any suitablemeans. Non-limiting examples of attachment means include: snapping thetransition onto the bottle via a plug seal; threading the transition onwith a plug seal; snapping the transition on and securing with glue;spin welding the transition onto the bottle; and combinations thereof

FIG. 13 illustrates another embodiment of a bottle 90 according to theinvention. There are differences between the embodiment in this figureand the one in FIG. 12. Specifically, the cap 40 in FIG. 13 comprisesexternal threads on an inner wall surface of a double wall 250 and thetransition comprises internal threads on its outer wall surface (threadsnot shown). In this way, the outer wall of the transition is not visiblewhen the cap and the transition are mutually engaged such that thebottle is sealed.

The bottle may be capable of containing a fluid composition.Non-limiting examples of useful fluid compositions include fluid fabriccare compositions. Such compositions include, but are not limited tofabric detergent, fabric enhancer and 2-in-1 fabric detergent andenhancer compositions. In some embodiments, the fabric care compositionis Compacted.

The bottle may be labeled using any suitable means. A non-limitingexample is the use of a shrink sleeve that may be fitted over the bottlebody. Useful means and configurations for shrink sleeving are describedin USPN: 2006/0141182A1, 2007/0095779A1 and US20050139568A1.

Method

The present invention is also directed to a method of sealing a bottlecontaining a liquid using the present, inventive threaded closureassembly. The method steps are found at p. 1, line 30 to p. 2, line 23.For the sake of brevity, they will not be repeated here. Notably, thismethod allows for the reduction of Off-torque necessary for a consumerto apply to the cap the first time it is opened. Without wishing to bebound by theory, it is believed that the particular selection ofmulti-lead threads, having unusually high thread lead anglesaccomplishes at least two highly desirable results. First, theOff-torque that is necessary to apply when removing the cap from abottle the first time is reduced as compared to caps having the samenumber of threads having typical thread lead angles. This isdemonstrated in the Data section below. Second, less twisting motion isrequired to seal the bottle. Both of these aspects can be of relevanceto consumers, particularly those consumers who suffer from lack ofmobility due to for arthritis for example.

Data

The Off-torque necessary for a consumer to apply to a cap the first timeit is opened may be measured using the following method. A cap isapplied to a transition utilizing a force that is typical of thatemployed in a bottle manufacturing line. The force used provides for aliquid tight seal between the cap membrane and the transition collarrim. The Off-torque required to unscrew the cap from the transition ismeasured using a torque gage as follows. First, the bottle is capturedin a fixture while a chuck attached to a torque gage is used to removethe closure. The Off-torque is the torque at which the closure isremoved.

Off-torque data is collected for three caps that are identical with theexception of the thread configuration. Referring to FIG. 14, each ofcaps 1000 “A”, “B” and “C” have a total height 1001 of 2.175 inches anda cap opening 1002 having a diameter of 2.82 inches. Each cap isdescribed by the angle θ formed at the theoretical intersection of aline 51 drawn through the thread 1014 a, b or c with a line 81orthogonal to the longitudinal axis 80 of each cap. Comparative cap “A”has a single thread and thread lead; the thread lead angle 1010 a is 1.8degrees. Comparative cap “B” has three threads each having a separatethread lead and a thread lead angle 1010 b of 3.85 degrees. According tothe present invention, cap “C” has three threads, each with a uniquethread lead and a thread lead angle 1010 c of 5.50 degrees. Theresulting off-torque data are plotted in against each other as shown inFIG. 15.

As can be seen from FIG. 15, adding multiple threads to a cap (e.g.,caps B and C) provides for lower off-torque than a single-threaded cap(e.g., cap A). Moreover, by holding the number of thread leads constantand by increasing the thread lead angle, the off-torque of the cap isreduced (see cap C vs. cap B).

Approximately 360 degrees of rotation are needed to remove Cap “A” froma transition. Approximately 160 degrees of rotation are needed to removeCap “B” from a transition. Approximately 130 degrees of rotation areneeded to remove Cap “C” from a transition.

Based upon the foregoing, it may be concluded that while the inventivecap “C” can be applied in the manufacturing facility to be liquid tight,it is easier for a consumer to remove than comparative caps “A” and “B”.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

All numerical ranges disclosed herein are inclusive and combinable.

Every document cited herein, including any cross referenced or relatedpatent or application is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

1. A cap for a detergent container, said cap being described by alongitudinal center axis, said cap comprising: a. a closed cap topdistally attached to a substantially circular cap opening via a cap wallhaving an inner cap wall surface and an outer cap wall surface, saidouter cap wall surface having a circumference C_(o); b. a substantiallycircular cap membrane disposed on said outer cap wall surface; and c. atleast two thread structures disposed on said cap wall surface along saidlongitudinal center axis between said circular cap membrane and saidopening, wherein each of said at least two external threads comprises:i. a discrete thread start disposed along said outer cap wall surfaceproximate to said cap opening; ii. a thread lead angle of from about 4to about 45 degrees; and iii. a length less than one half of C_(o). 2.The cap of claim 1, said cap having an Overflow Volume of less thanabout 85 ml.
 3. The cap of claim 1, wherein there is a distance alongsaid longitudinal center axis of less than about 40 mm between said capmembrane and said closed cap top.
 4. The threaded closure assembly ofclaim 3, wherein there is a distance along said longitudinal center axisbetween said cap membrane and said closed cap top that is greater thanabout three or more times the distance between said substantiallycircular cap membrane and said substantially circular cap opening. 5.The cap of claim 1, wherein at least one of said thread structures iscontinuous.
 6. The cap of claim 1, wherein at least one of said threadstructures is discontinuous.
 7. The cap of claim 1, said cap comprisingat least one dosing line.
 8. The cap of claim 1, comprising two externalthreads.
 9. The cap of claim 8, wherein each of said external threadsare discontinuous.
 10. The cap of claim 1, comprising three externalthreads.
 11. The cap of claim 10, wherein each of said external threadsare discontinuous.
 12. The cap of claim 9, said threads having a threadlead angle of from about 4.5 to about 15 degrees.
 13. The cap of claim11, said threads having a thread lead angle of from about 4.5 to about15 degrees.
 14. A cap for a detergent container, said cap beingdescribed by a longitudinal center axis, said cap comprising: a. aclosed cap top distally attached to a substantially circular cap openingvia a cap wall having an inner cap wall surface and an outer cap wallsurface, said outer cap wall surface having a circumference C_(o); b. asubstantially circular cap membrane disposed on said outer cap wallsurface; c. three external thread structures disposed on said outer capwall surface along said longitudinal center axis between said circularcap membrane and said opening, wherein each of said at least twoexternal threads comprises: i. a discrete thread start disposed alongsaid outer cap wall surface proximate to said cap opening; ii. a threadlead angle of from about 4 to about 15 degrees; and iii. a length lessthan one half of C_(o); wherein there is a distance along saidlongitudinal center axis between said cap membrane and said closed captop greater than about three or more times the distance between saidsubstantially circular cap membrane and said substantially circular capopening.